It is known that the development of the light-sensitive silver halides of photographic elements can produce color photographic images. A silver image is produced by means of an aromatic primary amino type developer compound in the presence of color couplers which react with the oxidized developing substance to form a dye in the areas corresponding to the silver image.
In the subtractive three-color photographic process, light sensitive color photographic elements are used which include, coated on a support base, one or more red-sensitive silver halide emulsion layers, one or more green-sensitive silver halide emulsion layers, and one or more blue-sensitive silver halide emulsion layers, wherein upon color development cyan, magenta and yellow dye images are respectively formed.
The couplers normally used to produce cyan image dyes derive from phenols and naphthols (as described in U.S. Pat. Nos. 2,367,351; 2,423,730; 2,474,293; 2,772,161; 2,772,162; 2,895,826; 2,920,961; 3,002,836; 3,476,563; 3,880,661; in French Pat. Nos. 1,478,188 and 1,497,043 and in GB Pat. No. 2,070,000). These types of couplers can be used either in photographic layers or in the baths. In the former case, when it is desired they do not migrate from a layer into another, they can have ballasting substituents and they can bear also hydrophilic or hydrophobic substituents if they must be introduced into photographic layers, respectively, dissolved in water or in an organic solvent. Upon reaction with the oxidation products of the aromatic primary amino type developing agents, such couplers give indoaniline dyes under consumption of four equivalents of silver ions per mole of dye and, preferably, two equivalents of silver ions per mole of dye when the reactive methine group (in the para position to the phenolic hydroxylic group) is substituted with atoms and groups which are splitted off during the coupling reaction.
In the practical use of the cyan dye-forming couplers in the photographic processings, the choice of such couplers is very important because some characteristics of the dyes formed after development, i.e. stability to light, heat and humidity, stability towards the reduction by ferrous ions present in the processing, depend upon the kind of the coupler used.
The loss of density due to an insufficient stability of the dye is a cause of color imbalance in the developed photographic material. Such loss occurs with indoaniline dyes when the bleaching and bleach-fixing baths have an insufficiently high redox potential (for instance when in the bleaching bath, containing ferric ions, there is a too high concentration of ferrous ions).
An aspect of the present invention is therefore to provide a new class of cyan dye-forming 2-equivalent couplers with characteristics suitable to an optimal use in the photographic materials.